1. Field of Invention
The present invention relates to a green contrast enhancement filter for CRT display devices in which small amounts of elements are present for coloring and controlling the transmission of an Nd.sub.2 O.sub.3 containing silicate glass. Particularly, it relates to a green glass filter having a sharp transmission peak in the wavelength range of 540 to 550 m.mu. having a peak transmittance of about 10 to 16% through which light of wavelengths outside the transmission peak does not or substantially does not pass, and to a green filter glass through which light having a wavelength of 610 to 620 m.mu. passes with a transmittance of about 2 to 4% together with the light of said transmission peak.
2. Description of the Prior Art
In Braun tubes for figure display screens, etc., phosphor P-43 is often used as a fluorescent film on the inner face of the display. This phosphor has luminous peaks near 430 m.mu. (blue), 545 m.mu. (green) and 615 m.mu. (red), and these three color luminescences are joined to obtain white light, by which display is accomplished in black and white. The black-white display, however, has the fault that the figures often flicker and are obscure. In order to overcome this defect, though attempts have been made to improve the cathode ray tube (CRT) itself or to provide a gray plate on the front face of the display panel. These attempts are not fully developed as yet.
It has been found that it is most effective to lay a green glass filter having a sharp transmission peak on the front face of the display screen in order to overcome the above described faults. It is most preferred from the viewpoint of facilitating reading to display with red light of about 615 m.mu. and lay a glass plate which absorbs light of 600 m.mu. or less over the screen when the reading is carried out in the dark. It has also been found that a CRT display device having standard luminance shows the most excellent contrast and provides a clear-image without flickering when the peak transmittance of the filter is about 10 to 16% for green light and 2 to 4% for red light.